1. Technical Field of the Invention
The present invention relates to a method and an apparatus for automatic sampling and for performing an automatic image analysis to determine a particle size distribution, shape characterization and shape distribution.
2. Description of Related Art
It is important for example in the fertilizer industry to have reliable information about the end product size distribution and particle shape, as optimal values for these parameters are of importance both from a purely economical point of view and when using the product, e.g. when spreading the produced prills or granules. Furthermore, a process will be most economical if it gives a product with a narrow sieve span, without having to sieve away large fractions that have to be run in return.
A method and apparatus for this use is known from U.S. Pat. No. 5,011,285. The method includes the collection of particle samples and the generation of a particle curtain in a monolayer form. The particle curtain is formed by taking particles through a silo down onto a vibrating plate. The particle curtain is lit up and the images of the particles therein is recorded and analyzed. The silo has at least one level sensor to record the level of particles in the silo and to give a signal to the sampler.
In U.S. Pat. No. 5,309,215 there is also shown an apparatus for the determination of particle size distribution based on the same principle. Particles are fed from a sample collection chamber to a conveyor band or vibrating channel forming a particle curtain when falling down from this band or channel.
Both of these methods are dependent on a separate collection of the samples. The samplers commonly used in such processes are conveyor belt samplers comprising for example a container with a longitudinal slit that passes across the product stream on the conveyor belt or collects the samples at the end of the conveyor belt in such a way that the particles can fall gravimetrically into the sampler when it traverses the product stream. Also in production pipes, samplers collect particles from a cross section of the product stream.
The samples thereafter have to be transferred to the container/sample collection chamber before they can be analyzed. To install such a sampling and analyzing system often involves comprehensive reconstruction of the production line to fit a sampling system, if at all possible. For example by installation of an end of a conveyor belt sampler, the end of conveyor belt housing (covering) has to be reconstructed to fit the sampling system. The expense of such a comprehensive reconstruction of the process line can be a reason not to invest in an imaging analysis equipment. For some installations it could also be very difficult to find space in the process line for a sampling system or to find a sampling system that could be used in an existing process.